Abstract
The acid-base equilibria of an optical probe, 5-N, N-dimethylaminonaphthalene-1-sulfonyl group, conjugated to amino end groups of undrawn and drawn nylon 6 films have been investigated by the change of fluorescence intensity in aqueous NaCI solutions. The behaviors of acid titration of the conjugated films which had been treated in different conditions to remove the unreacted probe were distinguishable. The apparent pK values of the conjugated probe decreased with decreasing pH and were held constant below pH 2 except in some cases of the treatments. In addition, these pK values were rather lower than that of the probe itself in aqueous solutions. These phenomena were accounted for by the difference in the electrostatic potential between nylon 6 film and bulk water. This view was supported by the fact that pK values in 0.5 M NaCl solution were larger than those in water or in 0.05 M NaCl solution.
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